Glomeruli are the initial site of synaptic integration in the olfactory pathway. Axons from olfactory receptor neurons expressing the same odorant receptor project to the same one or few glomeruli in the olfactory bulb, where they synapse on the dendrites of mitral/tufted (MT) cells and glomerular interneurons. Odors are rep- resented by static patterns of glomerular activity ('maps'). Odors are sampled by sniffing. This imposes a strong temporal structure on the pattern of input to olfactory glomeruli. Thus, in addition to spatial organization, the temporal structure of ON input to glomeruli contains odor information. Temporally distinct patterns of ON input to glomeruli shape the postsynaptic processing of olfactory information. Patterns of glomerular in- put are transformed into output signals to olfactory cortex. This input-output function is shaped by OB inhibitory circuits. We will test the hypothesis that the operations of OB inhibitory circuits incorporate both spatial and temporal information to shape OB output. We have identified four distinct inhibitory networks in the glomerular layer. Two of these are intraglomerular, operating at the level of single glomeruli. Another, the interglomerular circuit, links 100's of glomeruli in a circuit that uses lateral inhibition to enhance contrast at the level of inputs to MT cells. A new multiglomerular circuit'inks smaller numbers neighboring glomeruli (modules?) that may be responsive to structurally similar odors. ET cells link ON inputs to all these inhibitory circuits. ET cells intrinsically burst in the range of sniffing frequencies and are entrained by repetitive ON input. Thus, they are ideally suited to endow glomerular inhibitory circuits with dynamic characteristics to encode j the temporal structure of olfactory input. This research investigates the static and dynamic properties of OB inhibitory circuits. Aim 1 Tests the hypothesis that ET cell bursting amplifies synaptic input. Aim 2 Elucidates the organization, function and activity-dependence of a new multiglomerular circuit. Aim 3 Tests the hypothesis that intra- and inter-glomerular circuits are dynamically regulated. Aim 4: Investigate the roles of concentration and sniffing to odor glomerular coding. Odors are sensed by sniffing but little is known about, how sniffing influences olfactory coding at the neural network level. The present research advances our understanding the role of active sensing in odor perception.;The research may indicate how learned sniffing strategies might compensate for reduced odor sensitivity in diseased or aged populations.